Topic: Graupner mini jet drive 2349 (Read 14942 times)

tobyker · « **on:** May 18, 2009, 11:14:16 am »

I've wanted one of these since I was about 12, and thought others might be interested to see what you get in the packet. To my surprise the jet comes as a kit - the wire is to make up the grille over the intake. It was far smaller than I thought, and the instructions say it is for use in "small to medium-sized model boats". It is nicely made, and the ends of the UJ even have "3" and "3.2" moulded in so you know which end is for the drive shaft and which for the motor. The flange on the end of the body seems to be moulded to fit a 3mm thick transom, so I might have to cut it down a bit and maybe shorten the drive shaft a fraction. I can't quite work out where the forward thrust of the shaft is taken, and have a nasty feeling it's on the motor bearings. I think I've got a Czech styrene hull for a pilot boat in the shed somewhere.....

I remember jet drives as the Dowty turbo jet, but they were developed by a farmer called Hamilton in NZ. Google for further info - there's a picture of a Gulf of Mexico ORSV with 4 jet drives on the web site. That would be interesting!

Martin (Admin) · « **Reply #1 on:** May 18, 2009, 11:43:13 am »

I know those guys! Their cousins do some work on my Bismarck on a slap dash basis.....

There was one of these drives on fleabay over the weekend, not cheap!

hopeitfloats · « **Reply #2 on:** May 18, 2009, 11:51:19 am »

i thought the same tobyker. i was so disappointed i never bothered finishing assembling mine. i couldnt see it moving a small boat let alone a medium sized.

Proteus · « **Reply #3 on:** May 18, 2009, 12:13:50 pm »

I looked at the shape of full size jets and there props, I could not understand why they have used such a poor design I did try to make a better prop but it needs to be cast with the revs it does. this would prob make it a far better unit.

hopeitfloats · « **Reply #4 on:** May 18, 2009, 12:53:39 pm »

the graupner unit is basically a shrouded propellor rather than a true jet impellor. no where near as efficient. it will be interesting to hear how tobykers unit goes though.

andrewh · « **Reply #5 on:** May 18, 2009, 01:57:33 pm »

tobyker

Are you the one with the hat?

Looks promising to me - the whole propulsion plan is to shift water backwards and travel forwards by reaction. Waterjets, like all jets and ducted fans work by low mass/high velocity wheras aircraft props and boat propellors work by high mass/low velocity.

What brushless are you aiming to apply to the shaft?
andrew
if andyN suggests a CMB90 - just say no!

andyn · « **Reply #6 on:** May 18, 2009, 03:18:24 pm »

Quote from: andrewh on May 18, 2009, 01:57:33 pm

if andyN suggests a CMB90 - just say no!

Nah, I would reccomend ditching the whole idea and getting a Zenoah / Sikk / RCMK and one of these:

http://www.prestwich.ndirect.co.uk/jetdrives.htm

andrewh · « **Reply #7 on:** May 18, 2009, 03:26:17 pm »

I believe that's the one with the afterburner

Are you, Andy a believer in the "if a little is good; more is better and too much is just enough" school of motor selection?
andrew

andyn · « **Reply #8 on:** May 18, 2009, 03:30:58 pm »

I am indeed. That's why the next boat I'm bulding is 39 inches long, 13 wide, and fitted with the aforementioned CMB 90...

hama · « **Reply #9 on:** May 18, 2009, 03:39:24 pm »

Tobyker!
I put one of these in my Model Slipway FSB Tenby. I use a 400 motor and it's enough speed for me, the jet is designed for a 500 motor so I think you can get decent speed out of it. It's a small jet designed for small boats, anybody who want something for bigger boats get a bigger jet as there is a wide range of jets from Graupner and Kehrer for instance. My only issue with this jet so far is that it's leaking a little bit through the shaft sealing, but it's no big deal. Good luck with your build, and please let us know how it goes!
Hama

tobyker · « **Reply #10 on:** May 18, 2009, 06:33:34 pm »

Cheers, Hama - it was your Tenby that inspired me, and I was wondering about doing the ASRL (sacrilege!) until I remembered about the spare hull in the shed. Yours certainly seems to go well enough on the 400; I thought I'd try going Brushless and having read andrewh's brushless primer I have gone mad and ordered a 2835 Turnigy 3900kV thingy. This seems to be sold to the aero boys as a 380 replacement and does 100mph in some flying machine. It will presumably do 25k rpm on 7.2v unless the whole thing bursts into flames first (watercooling?). I may well have to find some fast electric loony to drive it for me. Still the whole point about building for me is to see what will work. Yes, Martin - I did see your H&S inspector on the Bismark and decided to get some of his mates in. The one with the red sweater is normally to be found steering a sailing barge (pic). The trouble with them is that you set them on to a job and go away, and when you come back they are still standing about exactly where you left them. I have now recruited a lady one who is in the process of leaving the police force - perhaps they will work harder when she is on the staff. I am ignoring the doubters and hoping to confound them - if Hama's Tenby hasn't done so already.

tobyker · « **Reply #11 on:** May 21, 2009, 06:11:56 pm »

I am just a bit hacked off: The diameter of the impellor boss at the rear is 7.42mm. The diameter of the bearing housing into which the impellor shaft fits is 7.47mm - a difference of 0.05mm, which is quite acceptable and shouldn't have much effect on the flow. However, between the two I'm expected to put a "thrust washer" with an o.d. or 8.8mm. I can't see this doing much for the efficiency of the unit. I note that in the destructions the o.d. of the washer is given as 6mm, so maybe I'd better have a word with Herr G.

hama · « **Reply #12 on:** May 21, 2009, 09:20:02 pm »

Hi tobyker!
Today I took my shaft out to grease it. You're right about the washer, I never thought about it before but it is a little to big. And what`s it for? The thrustforce goes the other way and there is nothing there to take it. I don't think I will put it back. Like you say the force goes to the motor. There should be a bearing where the shaft enters the prop tube. I'm also thinking about the possibility to make a oiler tube or something. Keep us posted on your progress!
Hama.

tobyker · « **Reply #13 on:** May 22, 2009, 08:02:26 pm »

I suspect this may turn into a build thread, but no doubt Martin will move it if he thinks fit.
If you leave the washer out, hama, check the back bearing after a few runs just to see if there are any signs of wear -plastic to plastic at 20k rpm might be interesting, if they do touch.
I'm getting nearer mounting the jet body in what may be a rather unsuitable hull - so I'll post pictures of that later when I've made it look prettier. In the meantime, here are some pictures showing how I am mounting the motor on the unit. The mounting holes on the motor and the jet unit did not line up at all, and if I'd cut the jet body for the screw heads I'd have taken a lot of strength out of it. So i've made up some hooks to hook into the front mounting holes and pulled the motor onto them from the back. I had to locate the front of the motor as it didn't have a boss around the shaft to fit the hole in the jet, so I cut a ring out of 40 thou plasticard to fit the motor and match the od of the motor mount. I hope I've got it all concentric.

The other plasticard rings are to go on the after spigot of the jet body , on the outside of the transom. The spigot enters 1mm into the outlet pipe. As built there is about 4mm allowance for a transom, whereas mine is only about 1mm thick. I'd thought of cutting the spigot down, but that would move the rear bearing in the outlet, and hence the impellor, about 2mm forward. Looking at the impellor in place it maintains the best tip to body clearance if left as designed, so I decided to add wshers on the transom to make it all fit snugly. In the event I needed one 1mm and one 0.5mm plasticard washer. I hope to make some stabilit express or equivalent up tonight and put the jet body in the hull.

Captain Jack · « **Reply #14 on:** May 22, 2009, 10:41:57 pm »

I have two of these in My American Enterprise....good scale speed, but they were a pain to install.

Circlip · « **Reply #15 on:** May 23, 2009, 10:46:14 am »

Well, the Gropener units look a darned sight more refined than the "Taplin-Baker" hydrojets WE had to contend with, Luxury!

Regards Ian.

Proteus · « **Reply #16 on:** May 23, 2009, 11:23:11 am »

you can buy a adapter ring to make smaller brushless motors fit, most brushless motor stockists have them , the revs that a motor runs at you may have it moving about with that method of holding the motor, they are only cheap, or just make one from am ally disk .

Proteus

tobyker · « **Reply #17 on:** May 23, 2009, 02:10:07 pm »

That was indeed my first thought but I would not have been able to make such an adapter ring with sufficient accuracy - let alone find suitable screws, and I didn't know they were commercially available. I'll stick with my bodge for the time being, and if the boat looks like working reasonably well, may retrofit one. Thanks for letting me know about them.

tobyker · « **Reply #18 on:** May 24, 2009, 10:44:45 pm »

The thrust washer is only plated brass, so that's soon sorted with a little file.

Martin (Admin) · « **Reply #19 on:** May 25, 2009, 07:11:30 am »

Quote

I suspect this may turn into a build thread, but no doubt Martin will move it if he thinks fit.

We'll keep it here for now Tobyker..... 'cause I think of a better place to move it too!?!

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Author Topic: Graupner mini jet drive 2349 (Read 14942 times)

hopeitfloats

Proteus

hopeitfloats

andyn

andyn

hama

hama

Captain Jack

Proteus